The biological fermentation process which produces methane and other gases from sewage and other organic waste materials is a natural process and can operate without the help of man-made apparatus. The use of suitable apparatus, however, can speed up gas production, make the process more efficient, and provide storage means for the combustible gases. An ideal process which can use anerobic bacteria for the production of methane includes the use of sewage, garbage, and cellulose waste products as basic materials. The process also preferably includes the use of solar energy and wind energy to heat the generating mass to an optimum termperature which lies within the range of 85.degree. F. to 95.degree. F. (29.5.degree. C. to 35.degree. C.).
In order to maintain a proper temperature throughout the day and night in northern countries during the winter months, it is necessary to combine the radiant energy from the sun with some other form of energy. The additional energy may be derived from heat exchangers operated by burning methane, natural gas, etc. or by using wind power to move paddles within the operating slurry to generate heat by mechanical friction. The use of paddlewheels in the slurry also serves to break up any encrusted solid material which may be moved to the surface of the slurry, bouyed up by the minute bubbles of generated gas. The paddlewheel motion releases the bubbles and permits the encrusted material to sink to the bottom of the tank. The fully digested material can then be drawn periodically from the bottom of the container and used as fertilizer. An arrangement of temperature control units, to be described in detail later, is used to maintain an optimum operating temperature automatically and to make full use of solar energy.
One of the features of the present invention is the apparatus which automatically adjusts for an optimum termperature in the digester container.
Another feature of the invention is the use of radiant energy from the sun to heat the slurry in the digester container.
A further feature of the invention is the use of a plurality of paddlewheels turned by wind power, to add frictional heat to the slurry.
Still another feature of the invention is the use of magnetic eddy currents to provide heat for the digester slurry.